It's flu season, but it's also RSV season. The lesser known ailment, respiratory syncytial virus, or RSV, infects the lungs and breathing passages. It is so common, according to the Centers for Disease Control, that almost every child will get it before he or she turns 2. But knowing it is common does nothing to calm the fears of a parent whose child is struggling to breathe.

Angela Tucker didn't know how sick her 6-month-old son, Kenny, was when she took him to the doctor. A previously healthy, full-term baby, he had a fever and stuffy nose. The doctor sent the Tuckers home with instructions for nebulizer treatments every four hours of albuterol, designed to help him breathe.

Within a few days, Tucker brought her son back to the doctor, worried he wasn't himself. His fever was back, and he was panting. His blood oxygen saturation level, which should be 100 percent or close to it, was in the 70s. The Tuckers rushed to the hospital, where Kenny was eventually intubated and placed in a medically induced coma at Albany Medical Center. He was there for nine days.

Tucker keeps a photograph of her son, now 4, hooked to tubes as a reminder of how quickly cold-like symptoms can turn deadly serious.

RSV is spread when someone carrying the virus coughs or sneezes into the air and someone else breathes it in. The virus is often the underlying cause of bronchitis and pneumonia.

Florence Nolan, a doctor with Adirondack Pediatrics in Glens Falls, said RSV is particularly dangerous for premature babies, whose lungs are not fully developed at birth, and for children with underlying health issues, like congenital heart disease. RSV will affect everyone else as nothing more than a cold, but while infected they can spread it by coughing and sneezing.

A lab test will confirm RSV, but there is no treatment for the virus. Treatment for babies with RSV is a matter of supporting the patient until he is over the initial stage — nebulizer treatments and oxygen. Not every baby with RSV will be hospitalized, that is only necessary when the baby isn't eating enough or his blood oxygen saturation level is too low, Nolan said.

For parents, the symptoms to look for are wheezing — a high-pitched noise when the baby breathes; retractions, which happen when the baby sucks in air so hard her ribs are visible. Retractions are more visible in babies six months old or younger. Finally, the baby will be irritable and look worried, Nolan said.

While there is no vaccine for RSV, there is a shot called Synagis produced by MedImmune. It is an immune booster, and lasts for 25 to 30 days, Nolan said. It is also expensive, between $3,000 and $5,000 per shot. Generally, insurance will only cover high-risk babies. Nolan said she keeps a list of eligible babies and contacts their families about the shot as RSV season, which runs from September to April, approaches. It has significantly reduced the incidence of RSV, she said.

The rules for prevention are the same as almost everything else: cover your mouth when you cough and sneeze. Wash your hands.

For Angela Tucker, it was hard not to feel paranoid. For months after Kenny came home from the hospital, she kept breathing masks around her house so she could cover his face with fabric. When RSV season came around again, she worried. Kenny has had the flu and pneumonia, but hasn't had another hospital stay.